Electrohydrodynamic Micropump and Its Use

ABSTRACT

An electrohydrodynamic micropump having at least one pumping passage for pumping a liquid, wherein there is at least one electrode device for generating an electrical alternating field and at least one device for producing a temperature gradient in the liquid to be pumped, which is arranged in and/or on the at least one pumping passage.

This invention relates to an electrohydrodynamic micropump according to the generic part of claim 1, a use of the micropump according to claim 36, and a method for pumping a liquid according to claim 37.

Pumps or micropumps which produce a pumping effect on liquids by applying electric fields are known. In particular, pumping systems have been described, whose pumping power is influenced by the cooperation of alternating electric fields and dielectric elements.

U.S. Pat. No. 4,316,233, for instance, discloses an apparatus for the transport of fluids or particles by means of an applied electric field. The apparatus consists of a pumping chamber with two electrodes, wherein a dielectric element with a sawtooth structure is arranged on one electrode. The specific arrangement results in the formation of a traveling electric field, whereby the fluid to be pumped is polarized and a pumping force is generated in the direction of the traveling field.

DE 103 29 979 A1 likewise describes a pump which includes a pumping chamber with an electrode device for generating an alternating electric field and a dielectric element. The dielectric element influences the field lines of the alternating electric field, wherein the pumping force necessary for pumping is generated by the alternating electric field. The dielectric element is formed such that the alternating electric field has a stationary and time-independent field gradient inside the pumping chamber in pumping direction. As a result, a stationary and time-independent polarization gradient is produced in the liquid in pumping direction.

With this configuration, forces are generated which act both in pumping direction and against the pumping direction. The transport of liquid is caused by an unsymmetric construction of the dielectric element and of the entire pumping system. The unsymmetric construction of the dielectric element leads to the generated force prevailing in one direction, and there is a transport of liquid in pumping direction, wherein the pumping direction cannot be changed or reversed due to the specific construction.

What is also disadvantageous in the described pumping system is the increased flow resistance caused by the dielectric element, since the dielectric elements necessarily constrict the flow passage and thus increase the flow resistance F_(r)˜1/r⁴ according to the Hagen-Pouseuille law.

Therefore, it is the problem underlying the invention to provide a micropump with which the pumping direction is easier to control, the pumping direction can be varied as desired, and with which a higher flow velocity can be achieved.

In accordance with the invention, this object is solved by an electrohydrodynamic micropump with the features of claim 1.

Accordingly, the electrohydrodynamic micropump includes at least one pumping passage, wherein at least one electrode device for generating an alternating electric field and a means for generating a temperature gradient in the liquid are provided in and/or at the at least one pumping passage.

In a simple, but efficient way, the micropump in accordance with the invention provides for an improved control of the pumping direction and of the pumping rate. In dependence on the alternating electric field applied and on the kind of liquid used, the pumping direction and the pumping rate can be influenced selectively.

For instance, ionic physiological salt solutions with concentrations up to 200 mM, in particular between 15 and 150 mM, have a defined pumping direction upon application of an alternating electric field with a frequency below 20 and 200 MHz, respectively. With an increase of the salt concentration to above 200 mM and the resulting higher ionic strength, there will also be an increase of the frequency above which there can be a change of the pumping direction into the opposite direction.

If non-ionic liquids such as e.g. hydrocarbons with a chain length of C₁₀ to C₁₉ are used, there can also be a reversal of the pumping direction at the same frequency of the alternating electric field applied.

Upon application of the alternating electric field, the electrode device furthermore acts as a heating element. At least one electrode of the electrode device acts as a heat sink, which results in the formation of a temperature gradient in the liquid to be transported, in particular in the vicinity of the electrode device. The temperature gradient causes the formation of a gradient of the conductivity and/or of the dielectric constant in the liquid to be transported. In the alternating electric field generated, the liquid experiences a resultant force in the direction of lower conductivities or dielectric constants due to the gradient, which results in a transport of liquid.

In addition, the flow resistance is reduced considerably due to the absence of the dielectric element. The at least one pumping passage can even be broadened as desired, in order to generate a larger volume flow.

Furthermore, the pump in accordance with the invention does not require a stationary, time-independent field gradient and hence no dielectric element for influencing the electric field lines between the electrodes.

Advantageous constructions can be achieved when the at least one electrode device and the at least one means for generating the temperature gradient are coupled. Such coupling can for instance be effected in the form of an integration in one component.

A simple guidance of the flow is obtained when the at least one pumping passage is at least partly formed linear. More complex constructions can be realized when the at least one pumping passage includes two or more segments. At least two linear segments can include an angle between 0° and 180°, in particular 90°.

Advantageously, the arrangement of the segments and the electrodes is chosen such that the inflow of a liquid is effected substantially vertical to the electric field lines. It is also advantageous when the arrangement of the segments and electrodes is chosen such that the outflow of a liquid is effected substantially parallel to the electric field lines.

The flow can be influenced in a positive way, when in the transition region of at least two segments at least one flow guiding means, in particular of a dielectric material, is arranged. The flow guiding means can prevent e.g. an otherwise occurring circular flow. Advantageously, the at least one flow guiding means constitutes a constriction of the flow cross-section for the flowing medium, in particular has a wedge-shaped cross-section.

The electrode device of the pump in accordance with the invention preferably includes at least one first and at least one second electrode, which are located opposite each other, wherein the electrodes are arranged as plates flat on the bottom, wall and/or ceiling of the at least one pumping passage of the micropump. The flat arrangement provides for an overflow of the liquid to be transported, so that a further reduction of the flow resistance is achieved.

The electrode device can include at least one electrode, which is at least partly surrounded by the flowing medium. In such an arrangement, the electrode device includes at least one grating or at least one wire mesh as electrode, which is traversed by the flowing medium.

In principle, all electrode materials can be used as electrode material. Advantageously, however, the electrode device comprises at least two electrodes, in particular metallic electrodes with a high thermal conductivity. Particularly advantageously, the electrode device comprises at least two electrodes, in particular metallic electrodes, with different thermal conductivity. Advantageously, at least one of the electrodes has a high thermal conductivity. Preferred electrode materials include gold, platinum, indium tin oxide or further metals or metal oxides with a high thermal conductivity (e.g. greater than 20 W/(m K)). In principle, polymers can also be used. The very high thermal conductivity of a metallic electrode contributes to an increase of the temperature gradient and thus enhances the pumping power.

Advantageously, the first and second electrodes have dimensions and/or shapes different from each other. Preferably, the first electrode is characterized by a greater surface area, width and/or greater volume than the second electrode. The different dimensions lead to the formation of a stronger temperature gradient, since the greater first electrode has a supporting effect in its function as an additional heat sink in the system.

Advantageously, in at least one pumping passage at least one heating element is provided for generating an additional temperature gradient in the liquid, wherein the heating element preferably is located, depending on the frequency of the field, in flow direction before or behind the electrode device.

The additional temperature gradient generated by the heating element reaches into the region of the alternating electric field generated by the electrode device and supports the formation of a gradient of the conductivity and of the dielectric constant in the liquid to be transported.

The advantage of this arrangement consists in that the specific arrangement of the heating element in flow direction before or behind the alternating electric field generates pumping forces in only one direction. This leads to a considerable increase in efficiency.

In an advantageous embodiment, the at least one heating element and the second electrode are at least partly combined in the form of a common component.

The alternating electric field generated continuously and/or in a pulsed manner advantageously has a sinusoidal or rectangular time behavior. Preferably, the frequency of the alternating electric field is adjusted to an electric resonance frequency of the pump.

Each electrode of the pump inherently constitutes a capacitive element. In a pump with two opposed electrodes, the pumping medium can be interpreted as a dielectric of a conventional capacitor. If the pumping medium is e.g. water, its relative dielectric constant at room temperature is about 78. The supply lines can be interpreted as inductances (coils). Since they are electrically connected in series with the (electrode) capacitor, this is a series resonant circuit (suction circuit), i.e. under resonance conditions the voltage across the capacitor, i.e. on the electrodes, is magnified, and the pumping effect is enhanced. This enhancement also can occur very locally, in particular when the resonance condition along the electrode inside the pumping structure is satisfied only locally due to the inductance of the electrode itself. In this connection, it should be noted that the effective inductance of the electrode line surrounded by medium is approximately increased by the factor of (root of relative dielectric constant) (shortening factor). When using water, there is an increase by the factor of about 9.

Due to the outer wiring of the pump, in particular an additional inductance, the self-resonant frequency of the system can be adjusted. The fact that there is a maximum pumping effect under resonance conditions and that the dielectric constant in turn depends on the medium itself and its temperature, can be utilized for control effects. The resonance condition can for instance be adjusted such that the pumping effect reaches a maximum, when an undesired medium or object is present inside the pumping structure in the case of media mixtures, emulsions or suspensions.

The heating element advantageously is provided in the form of heating structures, heating wires and/or thermal radiators. The heating elements or heating structures preferably are produced together with the electrode device in one manufacturing process.

Advantageously, the liquid to be transported by means of the pump is characterized by a conductivity of 0.0001 S/m to 10 S/m and a permittivity of 0.6 to 10000.

The at least one pumping passage of the micropump advantageously is arranged on a microsystem, in particular a chip. Examples for biological or chemical microsystems or chips are known for instance under the names “factory on a chip”, “Lab-on-Chip” or “micro-total analysis system”.

The chamber advantageously is filled with chemical and/or biological reaction systems, such as nutrient solution, cell cultures, physiological salt solutions, suspending agent and/or chemical reaction solutions. The micropump provides for a transport or movement of the reaction solutions inside the chamber and thus substantially acts in the form of a microstirrer.

It is conceivable that in one embodiment chemical reactions are performed or peptides are modified in the microreactor chamber. It is also conceivable that cells are grown in such structure. An encapsulation of substances or cells and the transport thereof in this system also is possible when using long-chain hydrocarbons as pumping liquid. In this case, the cells are enclosed in aqueous droplets which are emulsified in the organic pumping liquid.

The microreactor chamber advantageously is filled or evacuated by means of a microdosing system. The microdosing system constitutes for instance a piezo element, piezo actuator with corresponding valves.

The micropump—with or without said microreactor chamber—can also be integrated in a pumping structure or pumping system comprising at least one pumping chamber and at least one discharge chamber,. Advantageously, the pumping chamber opens into the at least one pumping passage on at least one discharge opening. The at least one pumping passage, in which the electrode device and possibly a heating element are arranged, in turn advantageously opens into the discharge chamber on at least one outlet opening. The discharge chamber likewise can be used for receiving biological and/or chemical reaction solutions, e.g. for growing cells.

The discharge chamber advantageously is connected with at least one further passage, whereby the micropump can be used e.g. for spreading substances or materials in the microsystem of the pumping structure. The pumping chamber and the discharge chamber advantageously are also connected via the at least one pumping passage and the further passage. The further passage preferably can constitute a measurement channel, reaction channel and/or supply channel.

In general, the pumping chamber, the at least one pumping passage, the discharge chamber and the further passage advantageously form a closed circulation system, wherein the at least one pumping chamber and the discharge chamber each include at least one inlet and/or outlet passage for filling and/or evacuating the circulation system.

The object of the invention also is solved by a use of the pump according to claim 36 and a method with the features of claim 37.

Accordingly, the micropump with the features according to claims 1 to 35 is used for pumping liquids, in particular in closed circulation systems.

The method of the invention for pumping a liquid in a micropump according to at least one of claims 1 to 35 is characterized by the formation of an alternating electric field and a temperature gradient in the liquid to be pumped between at least two electrodes, wherein the pumping direction is controlled by the frequency of the alternating electric field applied and/or by the temperature gradient in the at least one pumping passage.

The method of the invention advantageously is also characterized by the formation of an additional temperature gradient in the at least one pumping passage by a heating element, wherein the temperature gradient reaches into the region of the alternating electric field between the electrodes or wholly or partly overlaps with the same.

The invention will be explained in detail below by means of several embodiments with reference to the Figures, in which:

FIG. 1: shows a schematic representation of a first embodiment of the micropump in accordance with the invention;

FIG. 2: shows a schematic representation of a second embodiment of the micropump in accordance with the invention;

FIG. 3: shows a schematic representation of a third embodiment of the micropump in accordance with the invention;

FIG. 4: shows a schematic representation of a closed circulation system with the micropump in accordance with the invention;

FIG. 5: shows a modelled representation of the temperature profile (indicated in Kelvin) in a closed circulation system with the micropump in accordance with the invention;

FIG. 6: shows a modelled representation of the course of the force of flow (indicated in N/m³) in a closed circulation system with the micropump in accordance with the invention;

FIG. 7: shows a modelled representation of the flow rate (indicated in m/s) in a closed circulation system with the micropump in accordance with the invention;

FIG. 8: shows a first diagram with the experimentally obtained representation of the functional relation of applied frequency and velocity in dependence on the conductivity of the liquid to be pumped;

FIG. 9: shows a second diagram with the experimentally obtained representation of the functional relation of applied electrode voltage and velocity;

FIG. 10: shows a third diagram with the experimentally obtained representation of the functional relation of heating power and velocity;

FIG. 11A: shows a fourth embodiment with an angled pumping passage;

FIG. 11B: shows a detailed view of the fourth embodiment of the invention;

FIG. 12: shows a representation of a simulation result of the fourth embodiment;

FIG. 13A: shows a fifth embodiment of the invention with an angled pumping passage;

FIG. 13B: shows a detailed representation of the fifth embodiment;

FIG. 14: shows a schematic representation of a sixth embodiment;

FIG. 15: shows a representation of a simulation result (temperature, field strength) of the sixth embodiment;

FIG. 16: shows a representation of a simulation result (pressure distribution in the central region) of the sixth embodiment;

FIG. 17: shows a schematic representation of a seventh embodiment;

FIG. 18: shows a representation of a simulation result of the seventh embodiment;

FIG. 19: shows a representation of a simulation result of the seventh embodiment;

FIG. 20: shows a schematic representation of an eighth embodiment;

FIG. 21: shows a simulation result of an embodiment without a flow guiding means (wedge-shaped structure);

FIG. 22: shows an enlarged representation of a detail of FIG. 21;

FIG. 23: shows a simulation result of an embodiment with a flow guiding means;

FIG. 24: shows an enlarged representation of a detail of FIG. 23.

FIG. 1 shows the schematic structure of a first embodiment of the electrohydrodynamic micropump 1 of the invention, comprising a pumping passage 2 and an electrode device 6. In the pump, the electrode device 6 is arranged, which includes a first electrode 4 and a second electrode 5. The electrodes 4, 5 preferably are made of materials with different thermal conductivities. The alternating electric field generated and the temperature gradient generated between the electrodes exert a force on the charge carriers and/or dipoles of the liquid and thus generate a transport of liquid in or against the illustrated flow direction 7.

In FIG. 1, only a linear pumping passage 2 is shown. In principle, it is possible to provide a plurality of pumping passages 2, which also can have more complex shapes. For reasons of clarity, the passages illustrated in the Figures are shown in one plane, and it is possible to spatially arrange the individual components of the device. Thus, e.g. a plurality of pumping passages 2 might be realized in a three-dimensional arrangement with respect to each other.

In FIG. 1, the two electrodes 4, 5 are located opposite each other on both sides of the pumping passage 2, with other arrangements also being possible. In a further embodiment (see FIG. 11) it is shown that the electrodes can also be arranged in some other way relative to the pumping passage 2 and relative to each other. In the Figures, the electrodes 4, 5 also are shown only schematically.

In a passage with two opposed, flat electrodes 4, 5 of the same size and construction, a temperature maximum is obtained exactly in the middle between the electrodes 4, 5 when current flows between the electrodes 4, 5. The production of heat by the electric current is in equilibrium with a discharge of heat via the passage walls, via the electrodes 4, 5 themselves and via the adjoining liquid in the passage, which lies outside the electric field (see also FIGS. 12 and 15). This means that temperature gradients are obtained in the vicinity of the passage walls and in the surroundings of the electrodes.

The temperature gradients in the vicinity of the passage wall are vertical to the electric field lines and therefore have no effect (apart from the fact that a flow over the walls would not be possible). The temperature gradients in the surroundings of both electrodes extend parallel to the electric field and therefore interact with the electric field. There is produced a flow pointing away from the electrodes (at low frequencies).

In a symmetrical passage with two flat electrodes, a local circular flow can be obtained above the electrodes, but no resultant flow, as the forces in both directions should be equal. For producing a resultant flow, e.g. two approaches can be used:

-   -   1. the temperature field in the vicinity of an electrode is         influenced, e.g. by         -   a. a heating element, so that the temperature gradient is             reduced or even inverted at this point (the heat input of             the heater then dominates the temperature field).         -   b. the electrodes themselves, which have a different size             and/or are made of a material with a different thermal             conductivity.     -   2. incorporation of an inlet in the passage (see T-passage or         angled pump), which is located between the two electrodes and         through which the medium can flow in both directions over the         electrodes. In the latter case, both temperature gradients above         the electrodes are equally used.

As shown in approach 2, it is for instance important for generating a pumping force, how temperature gradient and electric field lines are located relative to each other. Only if the same extend substantially parallel, is a force exerted on the medium. In a T-passage, no force therefore is obtained in the direction of the inflow passage.

FIG. 2 schematically illustrates the structure of a second embodiment of the electrohydrodynamic micropump 1 with a pumping passage 2, a meander-shaped heating element 3 arranged in the pumping passage, and an electrode device 6 with the electrodes 4 and 5. By generating an additional temperature gradient by means of the heating element 3, the transport of liquid is supported.

A third embodiment of the pump in accordance with the invention is shown in FIG. 3, in which the second electrode 5 is combined with a portion of the heating element 3 to form a component 8. Broadening the first electrode 4 leads to an improved dissipation of heat and an increase of the temperature gradient and hence a higher flow rate.

A further embodiment of the micropump in accordance with the invention is incorporated in a circulation system 13 shown in FIG. 4. The circulation system 13 comprises the pumping chamber 9, the pumping passage 2 with the heating element 3 and the electrode device 6, the discharge chamber 10 and the further passage 11, wherein the further passage 11 can contain a chemical or biological system for practical applications. At the discharge opening 2 a, the pumping chamber 9 opens into the pumping passage 2 at right angle, which pumping passage merges into the discharge chamber 10 at a right angle at the outlet opening 2 b. The passage 11 likewise is arranged at right angles with respect to the pumping chamber 9 and the discharge chamber 10.

FIG. 4 shows a substantially rectangular, planar system of passages. In principle, it is also possible that the passages have more complex shapes and are spatially arranged with respect to each other.

In the embodiment shown here, the distance between the pumping passage 2 and the passage 11 is 100 to 2000 μm, preferably 1100 μm, and between the pumping chamber 9 and the discharge chamber 10 it is 50 to 1500 μm, preferably 900 μm.

These values only are exemplary and can also differ in other embodiments, corresponding to the object.

In the present embodiment, the circulation system 13 is filled at the inlet passages 12 with an aqueous liquid with a conductivity of 0.01 S/m and a relative permittivity of 80. Upon filling, the passages 12 are closed, so that no further liquid movement can occur in these directions. The pumping passage 2 has a height between 20 and 100 μm, preferably of 64 μm.

As shown in FIG. 4, the heating element 3 constitutes a meander-shaped heating coil. By applying a voltage (d.c.) of 1.5 V, the liquid is heated to a temperature of more than 312 K, whereby a temperature gradient is formed in the pumping passage 2 in accordance with the model shown in FIG. 5.

The electrode device 6 includes two electrodes 4, 5 extending flat on the ground with a thickness of 10 to 1000 nm, preferably 100 nm, whereby the liquid can flow over the electrodes without an additional resistance. By applying an alternating voltage (a.c.) of 30 Vrms with a frequency of 300 kHz, a strong electric field is obtained between the electrodes. In accordance with the model shown in FIG. 6, the liquid in the electric field experiences a force up to 1169 N/m³ in the direction of a lower conductivity or lower temperatures and thus is moved along the pumping passage 2 in flow direction 7. A circular flow is formed from the pumping passage 2 through the discharge chamber 10 into the passage 11 and the pumping chamber 9. In the pumping passage 2 and in the passage 11, the flow rate exhibits the highest values of up to 1.646e*10⁻⁴ m/s in accordance with the model of FIG. 7.

FIG. 8 shows frequency spectra of liquids with different conductivities at an applied electrode voltage of 40 V and a heating power of 0.187 mW. As can be taken from the diagram, the velocity is constant over a wide frequency range. With increasing frequency, there will be a decrease in the pumping velocity and finally, at a liquid-specific value of 0 μm/s, a reversal of the pumping direction.

In FIG. 9, the pumping power or velocity of two liquids with different conductivities is graphically represented in dependence on the applied electrode voltage. The measurements are made at a heating power of 0.187 mW and a frequency dependent on the conductivity of the liquid, wherein a frequency of 1 MHz is employed for a first liquid with a conductivity of 1117 μS/cm, and a frequency of 3 MHz is employed for a second liquid with a conductivity of 706 μS/cm. The velocity of the liquid to be pumped increases proportional to the applied electrode voltage.

FIG. 10 shows the influence of the heating power on the velocity of the liquid to be pumped, with a proportional relation being recognizable here as well. The velocity increases with increasing heating power. The measurements are made at an electrode voltage of 40 Vrms and at a frequency dependent on the conductivity of the liquid, wherein here as well a frequency of 1 MHz is employed for a first liquid with a conductivity of 1117 μS/cm, and a frequency of 3 MHz is employed for a second liquid with a conductivity of 706 μS/cm.

In FIGS. 11 to 24, further embodiments of the invention are shown, in which the pumping passages 2 include a plurality of segments 21, 22, 23.

Subsequently, in particular two variants of an angled, electrohydrodynamic micropump (subsequently briefly referred to as “angled micropump”) will be described. FIG. 11A schematically shows the structure of a first variant. There is used a T-passage, which includes three linear segments 21, 22, 23. The inlet 21 (here also referred to as measurement channel) merges into two outlets 22, 23, which are shown on an enlarged scale in FIG. 11B. The point of maximum force action is located directly at the bifurcation of the T-passage. In this embodiment, the passage height is 60 μm.

In FIG. 11A, a substantially T-shaped arrangement of three segments 21, 22, 23 is shown, which also is referred to as angled arrangement. By way of example, the linear segments 21, 22, 23 arranged in one plane are located at an angle of 90° with respect to each other, with other arrangements also being conceivable. In particular, the segments 21, 22, 23 also can be spatially arranged with respect to each other.

At the transition from the first segment 21 (measurement channel) to the two other segments 22, 23, a wedge-shaped flow guiding means 30 is arranged on both sides of the measurement channel, which guides the flow from the measurement channel 21 still a bit further into the two segments 22, 23, which are slightly constricted at the same time. In flow direction, the channel then expands again behind the segment 22, 23.

Two electrodes 4, 5 are arranged flat on the wall of the channel structure, substantially in the vicinity of the inlet through the measurement channel 21 and the two outlets 22, 23. A voltage (here e.g. an alternating voltage of 40 Vrms, 1 MHz) between the electrodes generates an electric field, and a current flows between the electrodes 4, 5. The flow of current heats the conductive solution in the segments 21, 22, 23 of the pumping passage between the electrodes and effects a temperature gradient pointing from the electrodes to the middle of the inlet passage.

In FIG. 12, the temperature gradients are illustrated as simulation result of a similar geometrical configuration. In this embodiment, the flow guiding means 30 differ from those of FIG. 11A. The temperature gradients are represented as arrows. The conductivity is 500 mS/m, and the electrode voltage is 30 Vrms.

In combination with the electric field, a force is exerted on the liquid, parallel to the electric field lines and against the direction of the temperature gradients, i.e. in the direction of the two outlet passages (see FIG. 11A, 11B).

The two wedge-shaped flow guiding means 30, which will be discussed in detail below, constrict the transition to the segments 22, 23 of the outlet passages, in order to minimize a local circular flow. By way of experiment, flow rates of about 25 μm/s can be measured in the measurement channel 21.

In FIG. 13A, a further embodiment is shown, whose flow guidance substantially corresponds to the embodiment of FIG. 11A, so that reference is made analogously to the corresponding description.

In the embodiment of FIG. 13A, the electrodes 4, 5 are arranged lying flat on the ground, wherein the electrodes 4, 5, however, extend into the two segments 22, 23 of the outlet passages. In the embodiment of FIG. 11A, on the other hand, the electrodes 4, 5 were arranged in the wall. FIG. 13B shows an enlarged representation of the T-shaped region. In such an arrangement, a flow rate of about 100 μm/s could be measured in the measurement channel 21, i.e. a velocity higher by a multiple than in the embodiment of FIG. 11A. The power supply to the electrodes 4, 5 was effected like in the embodiment of FIG. 11A.

The measurement channel 21 of the angled micropump guides the liquid to be pumped between the electrodes 4, 5 such that it flows in rather vertical to the electric field lines (see FIGS. 12 and 15 to 21), while the orientation of the segments 21, 22 of the outlet passage ensures an outflow rather parallel to the electric field lines. The temperature gradient in the region of the electric field should be rather steep and point from the outlet passage in the direction of the middle of the inlet passage.

As shown in FIGS. 14 to 19, the passage geometries can be varied, wherein at least one temperature gradient is obtained in the vicinity of the electric field, which extends parallel to the electric field and parallel to the outlet passage, and further temperature gradients have no effect, because they are either vertical to the electric field (e.g. inlet passage) or because the passage wall prevents a flow (e.g. the passage angled by 90° in FIG. 17-19).

A further embodiment is shown in FIG. 14. The same includes intersecting passages. The first segment 21 is represented vertical, from which two segments extend at right angles. In the representation of FIG. 14, the inflow is effected from above and from below through the linear segment 21.

In this embodiment, the electrodes 4, 5 are located in the vicinity of the points where the two segments 22, 23 open into the first segment 21. The electrodes 4, 5 are arranged flat on the wall, so that the medium can flow over the same. They lie flat on the wall, in the bottom or on the ceiling of the outlet passages 22, 23, alone or in combination. It is also possible to form the electrodes 4, 5 as a fine grating, which extends through the cross-section of the outlet passages and can be traversed by the medium.

In FIG. 15, the configuration of FIG. 14 is simulated. The electrodes 4, 5 are only shown as lines. The inflow of the flowing medium is effected vertical, the outflow parallel to the electric field lines. The temperature gradients (arrows) point to the middle of the segment 21 for the inlet passage.

In FIG. 16, the pressure field for this configuration is shown in the central region of a pumping system. The pressure gradient is greatest above the electrodes.

In order to move the liquid in the passages with a certain velocity, the pump must pump against the flow resistance of the passage walls. Before the point of the pumping effect, a negative pressure is obtained, because the pump sucks in the medium (liquid), and behind said point an excess pressure, because the pump urges the medium further through the passage. What is essential is the pressure difference. For the model calculation, the marginal condition was assumed that the pressure at the passage ends is 0. Hence, the inlet and outlet passages are at the same pressure level and short-circuited, so to speak. FIG. 16 only is a section of the model, which is why the values at the edges cannot be seen. The calculated model is greater than in FIG. 16, i.e. the passages are much longer. Thus, the medium can cover an appropriate distance, and the pump hence must work against the corresponding flow resistance. In this way, realistic flow velocities have been calculated. For very short passages, the calculated velocity would be distinctly higher.

On a representation of simulation results of the entire model, details would not easily be visible. What is important in FIG. 16 is the pressure difference above the electrodes 4, 5.

The number of the passages 21, 22, 23 can be reduced to one segment 21 for the inlet and one segment for the outlet. In FIG. 17, such configuration is shown for an orthogonal arrangement. The electrodes 4, 5 are arranged in the region of the second segment 22 and on the opposite wall of the first segment 21. The inflow is effected vertical and the outflow parallel to the electric field lines.

In FIG. 18, a simulation result of the configuration of FIG. 16 is shown. The electrodes are only represented as lines. The inflow of the flowing medium is effected vertical, the outflow parallel to the electric field lines. The temperature gradients (arrows) point to the middle of the segment 21 for the inlet passage.

In FIG. 19, the pressure field is shown for this configuration. The highest pressures are present in the first segment 21, so that there is a flow into the segments 22, 23 which extend from the first segment 21.

As already explained above, the passages can also be expanded spatially into the third dimension. In FIG. 20, a rotationally symmetric body with the axis of rotation along the outlet passage is illustrated with two segments 22, 23. The inlet passage is formed by a disk-shaped segment. The inlet segment 21 can serve as reaction chamber and also include more than two electrodes. The electrodes can be activated by different, phase-shifted signals.

In the illustrated embodiments of the angled micropumps, the arrangement of the segments of the pumping passages (inlet and outlet passages) 21, 22, 23 is such that an inflow is effected vertical and an outflow parallel to the electric field lines. Depending on the constructional variant, inlet and outlet passages therefore are connected as follows: In the case of one inlet and one outlet passage each with an angle of about 90° (FIG. 17). In the case of one inlet and two outlet passages (FIG. 11A) or two inlet passages and one outlet passage with a T-shaped bifurcation, and in the case of two inlet and outlet passages each with a 90° intersection. (FIG. 14, 17).

In the respective transition region from inlet to outlet passage (angle, bifurcation, intersection), an electric field is generated by two electrodes 4, 5, whose orientation satisfies the above condition for the transport of liquid.

This embodiment does not require an asymmetric temperature distribution between the electrodes 4, 5, which is generated by a heating element or electrodes of different thermal conductivity.

Subsequently, it will be described how the pumping effect can be enhanced by an e.g. wedge-shaped flow guiding means for shearing off a locally circulating flow (see FIG. 11A).

In particular on the inner edges of electrodes lying close to each other, local circular flows can form (FIG. 21), which always represent a loss of pumping power. FIG. 21 shows a two-dimensional simulation model of an angled micropump without wedge-shaped structure. The Figure shows the pressure (in Pa) and the circular velocity field in the liquid. The velocity in the measurement channel is 300 μm/s. The conductivity is 236 mS/m, and the electrode voltage is 30 Vrms.

Circular flows are obtained as soon as the forces acting in the passage cross-section differ in amount or direction (FIG. 22). FIG. 22 shows an enlarged view of the electrode edge. The acting force varies greatly in the region above the electrode edge.

To prevent or restrict a circular flow, the passage has been constricted at the point of the greatest force action (i.e. on the inner edges of the electrodes) by a wedge-shaped structure such that the return flow is largely sheared off (FIGS. 23 and 24). It should be noted that the wedge-shaped structure, the flow guiding means, is not a dielectric, but a hydrodynamic element.

FIG. 23 shows a two-dimensional model of an improved angled micropump with a wedge-shaped structure as flow guiding means 30. FIG. 23 shows the pressure (Pa) and the velocity field in the liquid. The circular flows are largely prevented by protrusions in the passage geometry. The velocity in the measurement channel was quintupled to 1500 μm/s. The conductivity is 500 mS/m, and the electrode voltage is 30 Vrms.

Similar to FIG. 22, FIG. 24 shows an enlarged view of the electrode edge of the model. The change of the acting forces is smaller in the region above the electrode edge.

LIST OF REFERENCE NUMERALS

-   1 electrohydrodynamic micropump -   2 pumping passage -   2 a discharge opening -   2 b outlet opening -   3 heating element -   4 first electrode -   5 second electrode -   6 electrode device -   7 flow direction -   8 component of a combination of the second electrode 5 with portions     of the heating element 3 -   9 pumping chamber -   10 discharge chamber -   11 further passage -   12 inlet and/or outlet passage -   13 circulation system -   21 first segment of a pumping passage -   22 second segment of a pumping passage -   23 third segment of a pumping passage -   30 flow guiding means 

1-38. (canceled)
 39. An electrohydrodynamic micropump comprising: at least one pumping passage for pumping a liquid flowing medium; at least one electrode device for generating an alternating electric field; and at least one heating device for generating a temperature gradient in the liquid to be pumped being arranged in and/or at said at least one pumping passage.
 40. The electrohydrodynamic micropump according to claim 39, wherein said at least one electrode device and said at least one device for generating the temperature gradient are coupled.
 41. The electrohydrodynamic micropump according to claim 39, wherein said at least one pumping passage is at least partly linear.
 42. The electrohydrodynamic micropump according to claim 39, wherein said at least one pumping passage includes two or more segments.
 43. The electrohydrodynamic micropump according to claim 42, wherein said segments are linear and disposed at an angle between 0° and 180°.
 44. The electrohydrodynamic micropump according to claim 42, wherein said electrode device includes at least two electrodes, and said segments and said electrodes are arranged such that the an inflow of the liquid flowing medium is substantially vertical to electric field lines generated by said electrode device.
 45. The electrohydrodynamic micropump according to claim 44, wherein the outflow of the liquid flowing medium is substantially parallel to the electric field lines.
 46. The electrohydrodynamic micropump according to claim 42, wherein said at least two segments have a transition region including at least one flow guiding member.
 47. The electrohydrodynamic micropump according to claim 46, wherein said at least one flow guiding member constricts a flow cross-section for the liquid flowing medium.
 48. The electrohydrodynamic micropump according to claim 39, wherein said electrode device includes at least one first electrode and at least one second electrode, said first electrode and second electrode are located opposite each other, and the liquid flowing medium flows between said first and second electrodes.
 49. The electrohydrodynamic micropump according to claim 39, wherein said electrode devices includes a first and second electrodes and the electric field is formed between said first and second electrodes in said at least one pumping passage.
 50. The electrohydrodynamic micropump according to claim 39, wherein said electrode device comprises at least two electrodes extending flat on at least one of a the bottom, ceiling or side wall of said at least one pumping passage.
 51. The electrohydrodynamic micropump according to claim 39, wherein said electrode device includes at least one electrode which is at least partly surrounded by the liquid flowing medium.
 52. The electrohydrodynamic micropump according to claim 39, wherein said electrode device includes an electrode which is one of a grating or one wire mesh and is traversed by the liquid flowing medium.
 53. The electrohydrodynamic micropump according to claim 39, wherein said electrode device comprises at least two metallic electrodes with a high thermal conductivity.
 54. The electrohydrodynamic micropump according to claim 39, wherein said electrode device comprises at least two metallic electrodes with different thermal conductivity.
 55. The electrohydrodynamic micropump according to claim 39, wherein said electrode device comprises at least two electrodes with at least one of different dimensions or shapes.
 56. The electrohydrodynamic micropump according to claim 39, wherein said electrode device comprises at least first and second electrodes, said first electrode has at least one of a greater surface area, a greater thickness or a greater volume than said second electrode.
 57. The electrohydrodynamic micropump according to claim 39, wherein said heating device comprises at least one heating element disposed for generating an additional temperature gradient and arranged in said at least one pumping passage.
 58. The electrohydrodynamic micropump according to claim 57, wherein said at least one heating element is arranged in said at least one pumping passage in a flow direction one of before or behind said electrode device.
 59. The electrohydrodynamic micropump according to claim 57, wherein said electrode device includes an electrode and said at least one heating element (3) and said electrode (5) are at least partly combined in one component.
 60. The electrohydrodynamic micropump according to claim 57, wherein said at least one heating element is a conducting microstructure with an electrically insulated surface comprising at least one of heating wires or thermal radiators.
 61. The electrohydrodynamic micropump according to claim 39, wherein the alternating electric field has one of a sinusoidal or rectangular time pattern and is generated one of continuously or pulsed.
 62. The electrohydrodynamic micropump according to claim 39, wherein the alternating electric field has a frequency which is an electric resonance frequency of the micropump.
 63. The electrohydrodynamic micropump according to claim 39, wherein said micropump has an additional inductive resonance system, in which the liquid flowing medium to be pumped is at least part of a dielectric of a capacitive element.
 64. The electrohydrodynamic micropump according to claim 39, wherein said at least one pumping passage is arranged on a microsystem comprising one of a μTAS-chip or a Lab-on-Chip system.
 65. The electrohydrodynamic micropump according to claim 64, wherein said at least one pumping passage is arranged in a chamber which comprises a microreactor.
 66. The electrohydrodynamic micropump according to claim 65, wherein said microreactor includes at least one of a chemical or biological reaction system.
 67. The electrohydrodynamic micropump according to claim 39, wherein said at least one pumping passage is coupled to a pumping system comprising at least one pumping chamber and at least one discharge chamber.
 68. The electrohydrodynamic micropump according to claim 67, wherein said at least one pumping chamber opens into said at least one pumping passage on at least one discharge opening.
 69. The electrohydrodynamic micropump according to claim 67, wherein said at least one pumping passage opens into said discharge chamber on at least one outlet opening.
 70. The electrohydrodynamic micropump according to claim 67, wherein said one discharge chamber is one of directly or indirectly connected with at least one further passage.
 71. The electrohydrodynamic micropump according to claim 70, wherein said pumping chamber and said discharge chamber are connected by said further passage.
 72. The electrohydrodynamic micropump according to claim 70, wherein said pumping chamber, said at least one pumping passage, said discharge chamber and said further passage comprise a pumping system which is closed at least for a time.
 73. The electrohydrodynamic micropump according to claim 72, wherein one of said pumping system or said chamber comprise a microreactor, and said microreactor is filled or evacuated by a microdosing system.
 74. A method of pumping liquids, which comprises: providing an electrohydrodynamic micropump for pumping liquids according to claim 39, and pumping liquids with the micropump.
 75. A method for pumping a liquid in an electrohydrodynamic micropump, comprising the steps of: forming an alternating electric field and a temperature gradient in a liquid being pumped between electrodes in at least one pumping passage; and controlling a pumping direction by a frequency of the alternating electric field applied and the temperature gradient in the at least one pumping passage.
 76. The method according to claim 75, including the further step of: forming an additional temperature gradient by using a heating element, and causing the additional temperature gradient to extend into a region of the alternating electric field between the electrodes or overlap the field wholly or in part.
 77. The electrohydrodynamic micropump according to claim 43, wherein said at least two linear segments are disposed at an angle of substantially 90°.
 78. The electrohydrodynamic micropump according to claim 46, wherein said at least two segments have a transition region, and at least one non-dielectric flow guiding member device dispose din said transition region.
 79. The electrohydrodynamic micropump according to claim 47, wherein said at least one flow guiding member has a wedge-shaped cross-section.
 80. The electrohydrodynamic micropump according to claim 42, wherein said one flow guiding member is a non-dielectric material.
 81. The electrohydrodynamic micropump according to claim 47, wherein said at least one flow guiding member has a wedge-shaped cross-section. 